Dynamic Changes in Endogenous Hormones in Rhododen- dron simsii Floral Organs

This study was conducted to investigate the dynamic changes of several hormones in Rhododendron simsii floral organs to provide theoretical basis for controlling its flowering period. A R. simsii variety ＂Purple Crane＂ was selected as the experimental material, and its flower organs were sampled at nine floral developmental stages to measure the contents of gibberellic acid-3 （GA3 ）, abscisic acid （ABA）, indole-3-acetic acid （IAA）, and zeatin riboside （ZR） through enzyme-linked immunosorbent assay （ELISA）. The results showed that the content of ZR was highest at full flowering stage; IAA and GA3 contents were higher than other stages in the process of flower bud differentiation and flowering. ABA played an important role in the regulation of flower bud formation. The results will provide theoretical references for exploring the regulation of plant hormones towards Rhododendron flower traits and breeding new varieties.

Analytical solutions of ground settlement induced by yaw in a space curved shield tunnel

This paper aims to provide the analytical solutions of the ground settlement for a space curved shield tunnel in the case of yaw construction.Settlement inducements include ground loss and construction loads,and two corresponding analytical models have been proposed in this study.Three-dimensional image theory has been adopted to calculate the ground settlement due to ground loss.Yawrelated parameters are introduced into the calculation model to deduce the relevant laws of the ground settlement.Based on modified Mindlin solutions,analytical models are established to calculate the ground settlement induced by construction loads,such as the frontal additional thrust,axial friction of shield shell,and the grouting pressure.The method of calculating the position of the shield machine in the ground is refined,and the influence area of construction loads from the shield machine is optimized.Subsequently,the obtained solutions are validated by a numerical model and field data.Besides,a comparison reveals that the proposed model is the composition of three classical analytical models,thus it excels them in solving the problem mentioned.Finally,parametric analyses of yaw are conducted to examine yaw angle and pitch angle on ground settlement.The proposed model can effectively predict ground settlement caused by the spatial linear shield tunneling process.

Analytical algorithms of compressive bending capacity of bolted circumferential joint in metro shield tunnels

The integrity and bearing capacity of segment joints in shield tunnels are associated closely with the mechanical properties of the joints.This study focuses on the mechanical characteristics and mechanism of a bolted circumferential joint during the entire bearing process.Simplified analytical algorithms for four stress stages are established to describe the bearing behaviors of the joint under a compressive bending load.A height adjustment coefficient,α,for the outer concrete compression zone is introduced into a simplified analytical model.Factors affectingαare determined,and the degree of influence of these factors is investigated via orthogonal numerical simulations.The numerical results show thatαcan be specified as approximately 0.2 for most metro shield tunnels in China.Subsequently,a case study is performed to verify the rationality of the simplified theoretical analysis for the segment joint via numerical simulations and experiments.Using the proposed simplified analytical algorithms,a parametric investigation is conducted to discuss the factors affecting the ultimate compressive bending capacity of the joint.The method for optimizing the joint flexural stiffness is clarified.The results of this study can provide a theoretical basis for optimizing the design and prediciting the damage of bolted segment joints in shield tunnels.

Bending failure performance of a shield tunnel segment based on full-scale test and numerical analysis

This study focuses on the bending failure performance of a shield tunnel segment.A full-scale test was conducted to investigate deformation and failure characteristics.During the loading,the bending failure process can be divided into four stages:the elastic stage,working stage with cracks,failure stage,and ultimate stage.The characteristic loads between contiguous stages are the cracking,failure,and ultimate loads.A numerical model corresponding to the test was established using the elastoplastic damage constitutive model of concrete.After a comparative analysis of the simulation and test results,parametric studies were performed to discuss the influence of the reinforcement ratio and proportion of tensile longitudinal reinforcement on the bearing capacity.The results indicated that the change in the reinforcement ratio and the proportion of tensile longitudinal reinforcement had little effect on the cracking load but significantly influenced the failure and ultimate loads of the segment.It is suggested that in the reinforcement design of the subway segment,the reinforcement ratio and the proportion of tensile longitudinal reinforcement can be chosen in the range of 0.7%–1.2%and 49%–55%,respectively,allowing the segment to effectively use the reinforcement and exert the design strength,thereby improving the bearing capacity of the segment.

Experimental investigation of face instability for tunnels in sandy cobble strata

In order to investigate the influence of face instability for tunnels with different burial depths in sandy cobble strata on earth pressure and the instability region,geomechanical model tests and numerical simulations were performed.The continuous excavation method was adopted to reduce the pressure of the soil bin and restore the real engineering situation.Earth pressure in three directions of the obser-vation section in front of the tunnel face was monitored during the tunneling of the shield.Evolutions of the lateral stress ratios at dif-ferent stages were also investigated.The instability area of the shield tunnel face in sandy cobble strata with different burial depth ratios during the instability stage was obtained based on the change ratio of earth pressure and compared with existing researches.The earth pressure began to change when the excavation was one shield diameter away from the observation section,and when the excavation reached the observation section,the earth pressure decreased significantly.The burial depth of shield tunnel in the sandy cobble strata has a significant impact on the evolution of soil arch and the size of the failure area.The numerical simulation of the continuum medium cannot reflect the stress redistribution characteristics of the granular body like sandy cobble strata,and the failure area or stress distur-bance area obtained by the model test is larger than the numerical simulation result.Existing methods have deviations in analyzing the failure area of shield tunnel face in sandy cobble strata.It provides not only guidance for shield tunnel excavation engineering in sandy cobble strata,but also a reference for the theoretical research on failure areas.

Influence of permeability anisotropy of seepage flow on the tunnel face stability

This paper focuses on the influence of permeability anisotropy of seepage flow on the face stability for a shied tunnel.An analytical model has been proposed to present the hydraulic head distribution around the tunnel face in the anisotropic ground,considering the difference of permeability coefficient in the horizontal direction and the vertical direction.The rationality of the proposed model is ver-ified by a series of numerical simulations.Then,an analytical model of face stability for a tunnel under the anisotropic seepage has been established based on the limit analysis upper bound method.Comparisons of the analytical solutions and the numerical simulations are conducted,and the limit support pressure of the two methods is consistent.The effect of permeability anisotropy and water pressure on the stability of the tunnel face is analyzed through the three-dimensional analytical solution.Anisotropy of permeability has a significant impact on the stability of the tunnel face,and its impact gradually decreases.It can also be found that the water pressure coefficient of the tunnel face has a significant effect on the limit support pressure and the failure area when the ratio of the horizontal permeability to the vertical permeability is large.

Three-dimensional theoretical analysis of seepage field in front of shield tunnel face

To evaluate hydraulic head distribution in front of a shield tunnel in a saturated soil layer,theoretical analysis and numerical simulations are carried out in this study.Based on the partial differential equilibrium equation of seepage flow,a three-dimensional(3D)theoretical analytical model of the shield tunnel face and the seepage field in front of it is established using the eigenfunction and the Fourier series expansion methods,and the hydraulic head calculation formula is derived.Combined with engineering cases,the theoretical analysis results and the 3D numerical simulation results are compared and analyzed.The effect of the water pressure of the tunnel face on the hydraulic head distribution is also analyzed.The results of the proposed analytical solution are in agreement with those of the numerical simulation solutions;moreover,the proposed analytical solution requires less time to calculate the seepage hydraulic head than the numerical simulation.The ratio of the initial water table to the diameter(D)of tunnel face has a more significant impact on the hydraulic head distribution at a position 0.5D above the tunnel vault.When the water pressure on the tunnel face is not considered,the values of the hydraulic head are significantly underestimated.

Bearing capacity and failure behavior of disconnectable coupling joint with double row wedges(DCJD)used in the prestressed internal bracing

A disconnectable coupling joint with double row wedges(DCJD)is a crucial component of the prestressed internal bracing in subway foundation pits.However,only a few studies have been conducted on the bearing capacity of the joints;moreover,the yield load and compression stiffness of DCJDs are typically determined from experience.The aim of this study was to quantitatively determine the bearing capacity and propose accurate formulas for calculating the yield load and compression stiffness of DCJDs.Hence,a DCJD was selected from a foundation pit in Beijing,China,and loading experiments were conducted under axial force.Load–displacement and load–strain curves were obtained,and the failure modes of the joint were analyzed.The experimental results were verified through several finite element models.Subsequently,parametric analyses were performed to investigate the effects of the dimensions of the key position on the DCJD’s bearing capacities.Moreover,regression analysis was used to obtain the formulae for estimating the initial compression stiffness and yield load of the DCJD.Finally,the fitting formulae results were compared with the numerical and experimental results.The comparisons showed that the fitting formulae were highly accurate in estimating the bearing capacity of the DCJD.